linux-kernel - Re: [PATCH 1/3] X86: Revamp reboot behaviour to match Windows more closely

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Date:	Thu, 9 Dec 2010 22:58:33 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, linux-acpi@...r.kernel.org, lenb@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] X86: Revamp reboot behaviour to match Windows more
	closely

On Thu, Dec 09, 2010 at 02:53:35PM -0800, H. Peter Anvin wrote:
> On 12/09/2010 02:51 PM, Matthew Garrett wrote:
>> I'm afraid I don't understand your argument. The date cutoff would be on
>> the order of 2001 (anything after this will have been tested with XP).
>> The spec that defines this behaviour only came into existence in August
>> 2000, and any older hardware will be missing the flag that indicates
>> that this feature is supported. It doesn't seem realistic to believe
>> that there's any real body of hardware that sets the flag but otherwise
>> has a broken implementation.
>>
>
> 2001 is probably a good date, then.
>
> It's pretty safe you'll see the bit being set on systems which are older  
> than that, even if it was not defined at the time it was created -- just  
> being garbage.  That's par for the course in BIOS land.

There's a revision field in the FADT. They'd need to simultaneously 
provide an incorrect revision *and* by pure luck set the 10th bit of a 
32-bit register. Is it possible? Yes. Is it likely? No, and I don't see 
a benefit in adding extra code to force hardware into a less-tested 
configuration.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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